1. Field of the Invention
The present invention relates to digital signal processing in a television receiver, and particularly relates to the improvement of a color demodulation system.
2. Description of the Prior Art
In conventional color demodulation systems, the clock signal which is used for A/D conversion has a quadruple subcarrier frequency (4F.sub.SC) phase locked to a color burst signal. Data of 4F.sub.SC in frequency are phase-shifted to be related to each other as (R-Y), (B-Y), -(R-Y) and -(B-Y). Every other piece of the data is extracted to perform color demodulation.
In conventional color demodulation systems, color demodulation can be performed even if the system receives an analog composite signal which is sent out from a video tape recorder, for example, and in which a color burst signal and a horizontal synchronizing signal are not synchronized with each other. However, since the video signal is subjected to A/D conversion through the use of the clock signal of the quadruple subcarrier frequency 4F.sub.SC in the system, the number of the samples of one line may not be 910. When signal processing is performed, such as scanning line interpolation and double writing into a memory to double a scanning line, the number of the samples of one line is not a fixed value locked to a horizontal period but fluctuates. This engenders problems such as manufacturing 1H delay lines. Also, system circuitry becomes complex.